Frances Hardinge is a children's author in the same way Lloyd Alexander, Diana Wynne Jones, or Sir Terry Pratchett is. Which is to say that while her protagonists may be children and her language is all family friendly, what she really writes are Stories That Everyone Should Read.
Fly by Night features the orphan Mosca Mye, black-eyed, by turns surly and naive, with a deep and desperate longing for reading. She's sort of like a Dickensian character, if Dickens had ever thought girls could have adventures too. She runs away from her village with a down-on-his-luck silver tongued conman (and occasional spy), Eponymous Clent, and a homicidal goose named Saracen.
I adore Mosca. I would hug her if I thought I could get away with it. She's prickly and suspicious and a loner. She can be very grudging about letting people know exactly what she's thinking. She is just starting to find out who she is and what she believes, but that doesn't make her dumb or credulous. She is not always brave or wise or gentle or nice, because she is thoroughly human. And Eponymous too. He can be cowardly just as often as daring and cynical just as often as romantic.
And Saracen is just pure awesomeness in goose form.
Just so you know, people die in this book. People change. People are betrayed in large and small matters, accidentally and purposefully, by "Good" characters and "Bad" ones. Not everyone has the same agenda. Things may not get wonderfully better in the future (although there is some hope). But there will be (the sequel is already out) further adventures, and that's all Mosca and I need.